• M.T.F. Pivi, R.E. Kirby, T.O. Raubenheimer
  SLAC, Menlo Park, California
• F. Le Pimpec
  PSI, Villigen

Any accelerator circulating positively charged beams can suffer from a build-up of an electron cloud in the beam pipe. The cloud develops through ionization of residual gases, synchrotron radiation and secondary electron emission and, when severe, can cause instability, emittance blow-up or loss of the circulating beam. The electron cloud is potentially a limiting effect for both the Large Hadron Collider (LHC) and the International Linear Collider (ILC). For the ILC positron damping ring, the development of the electron cloud must be suppressed. This paper presents the various effects of the electron cloud and evaluates their significance. It also discusses the state-of-the-art of the ongoing international R&D program to study potential remedies to reduce the secondary electron yield to acceptably low levels.

• A.W. Molvik, J.J. Barnard, R.H. Cohen, A. Friedman, M. Kireeff Covo, S.M. Lund
  LLNL, Livermore, California
• D. Baca, F.M. Bieniosek, C.M. Celata, P.A. Seidl, J.-L. Vay, W. Waldron
  LBNL, Berkeley, California
• J.L. Vujic
  UCB, Berkeley, California

Electron clouds and gas pressure rise limit the performance of many major accelerator rings. We are studying these issues experimentally with ~1 MeV heavy-ion beams, coordinated with significant efforts in self-consistent simulation and theory.* The experiments use multiple diagnostics, within and between quadrupole magnets, to measure the sources and accumulation of electrons and gas. In support of these studies, we have measured gas desorption and electron emission coefficients for potassium ions impinging on stainless steel targets at angles near grazing incidence.** Our goal is to measure the electron particle balance for each source – ionization of gas, emission from beam tubes, and emission from an end wall – determine the electron effects on the ion beam and apply the increased understanding to mitigation.

*J-L. Vay, Invited paper, session TICP; R. H. Cohen et al., PRST-AB 7, 124201 (2004). **M. Kireeff Covo, this conference; A. W. Molvik et al., PRST-AB 7, 093202 (2004).

• L. Wang, J. Wei
  BNL, Upton, Long Island, New York

Electron cloud due to beam induced multipacting is one of the main concerns for the high intensity rings because the electron multipacting becomes stronger with the increment of beam intensity. Electrons generated and accumulated inside the beam pipe form an "electron cloud" that interacts with the circulating charged particle beam. With sizeable amount of electrons, this interaction can cause beam instability, beam loss and emittance growth. At the same time, the vacuum pressure will rise due to electron desorption. This talk intends to provide an overview of the dynamics of the typical electron multipacting in various magnetic fields and mitigation measures in both long bunch and short bunch rings.

• E. Benedetto, E. Benedetto
  Politecnico di Torino, Torino
• G. Arduini, F. Roncarolo, F. Zimmermann
  CERN, Geneva
• B. Feng, A.F. Ghalam, T.C. Katsouleas
  USC, Los Angeles, California
• G. Franchetti
  GSI, Darmstadt
• K. Ohmi
  KEK, Ibaraki
• G. Rumolo
  CELLS, Bellaterra (Cerdanyola del Vallès)

• E.-S. Kim, Y.J. Han, J.Y. Huang, I.S. Ko, P.C.D. Park, S.J. Park
  PAL, Pohang, Kyungbuk
• H. Hukuma, H. Ikeda
  KEK, Ibaraki

• J.-L. Vay, M.A. Furman, P.A. Seidl
  LBNL, Berkeley, California
• R.H. Cohen, K. Covo, A. Friedman, D.P. Grote, A.W. Molvik
  LLNL, Livermore, California
• P. Stoltz, S.A. Veitzer
  Tech-X, Boulder, Colorado
• J. Verboncoeur
  UCB, Berkeley, California

Electron clouds and gas pressure rise limit the performance of many major accelerators. A multi-laboratory effort to understand the underlying physics via the combined application of experiment,* theory, and simulation is underway. We present here the status of the simulation capability development, based on a merge of the three-dimensional parallel Particle-In-Cell accelerator code WARP and the electron cloud code POSINST, with additional functionalities.** The development of the new capability follows a "roadmap" describing the different functional modules, and their inter-relationships, that are ultimately needed to reach self-consistency. Newly developed functionalities include a novel particle mover bridging the time scales between electrons and ions motion.*** Samples of applications of the new capability to the modeling of intense charge dominated beams**** and LHC beams***** will be shown as available.

*A.W. Molvik, these proceedings. **J.-L. Vay, Proc. "ECLOUD04," Napa (California), 2004. ***R.H. Cohen, these proceedings. ****P.A. Seidl, these proceedings. *****M.A. Furman, these proceedings.

• A.F. Ghalam, T.C. Katsouleas
  USC, Los Angeles, California
• E. Benedetto, F. Zimmermann
  CERN, Geneva
• V.K. Decyk, C. Huang, W.B. Mori
  UCLA, Los Angeles, California
• G. Rumolo
  GSI, Darmstadt

• K.G. Sonnad, J.R. Cary
  CIPS, Boulder, Colorado

• J.W. Flanagan, H. Fukuma, Y. Funakoshi, S. Hiramatsu, H. Ikeda, K. Ohmi, M. Tobiyama, S. Uehara, S. Uno
  KEK, Ibaraki
• E. Perevedentsev
  BINP SB RAS, Novosibirsk

• A.P. Shishlo, S.M. Cousineau, V.V. Danilov, S. Henderson, J.A. Holmes, Y. Sato
  ORNL, Oak Ridge, Tennessee
• S.-Y. Lee
  IUCF, Bloomington, Indiana
• R.J. Macek
  LANL, Los Alamos, New Mexico

The results of numerical electron-cloud simulations for long-bunch proton beams in accumulator rings are presented and compared with data from the Proton Storage Ring at LANL. The frequency spectra and growth rate of proton-bunch transverse instabilities are studied as functions of the RF cavity voltage, external magnetic fields, beam pipe surface properties, and other factors. We used the recently developed electron-cloud module in the ORBIT code. The model includes a fully self-consistent coupled treatment of the "proton bunch – electron-cloud" dynamics and the multipacting process with a realistic secondary emission surface model. Realistic lattices and proton bunch distributions are used. The efficiency of electron-cloud instability suppression has also been studied using a new ORBIT model.

• C. Vaccarezza, R. Cimino, A. Drago, M. Zobov
  INFN/LNF, Frascati (Roma)
• G. Bellodi
  CCLRC/RAL/ASTeC, Chilton, Didcot, Oxon
• K. Ohmi
  KEK, Ibaraki
• M.T.F. Pivi
  SLAC, Menlo Park, California
• G. Rumolo
  GSI, Darmstadt
• D. Schulte, F. Zimmermann
  CERN, Geneva

• C. Vaccarezza, R. Cimino
  INFN/LNF, Frascati (Roma)
• A. Giglia, N. Mahne
  ELETTRA, Basovizza, Trieste
• S. Nannarone
  UNIMORE, Modena

• H. Fukuma
  KEK, Ibaraki
• L. Wang
  BNL, Upton, Long Island, New York

• K. Ohmi, J.W. Flanagan, H. Fukuma, S. Hiramatsu, H. Ikeda, M. Tobiyama
  KEK, Ibaraki
• E. Perevedentsev
  BINP SB RAS, Novosibirsk

• M. Tobiyama, J.W. Flanagan, H. Fukuma, S.-I. Kurokawa, K. Ohmi, S.S. Win
  KEK, Ibaraki

• K.-I. Kanazawa, H. Fukuma, H. Hisamatsu, Y. Suetsugu
  KEK, Ibaraki

• Y. Golub
  MRTI RAS, Moscow

*Golub Yu.Ya. et al., in Nonlinear world: IV Intern. Workshop on Nonlin. and Turbul. Proc. in Phys., (ed. by V.G. Bar'yakhtar et al.) World Scientific Publishing Co. Pte. Ltd., Singapore, 1990, vol. 2, p. 857. **Golub Yu.Ya., Proceedings of EPAC 2002, Paris, France, p. 1253.

• Y. Golub
  MRTI RAS, Moscow

*Yu.Ya. Golub, N.E.Rozanov, Nuclear Instruments and Methods in Physics Research, A358 (1995) 479. **Yu.Ya. Golub, Proceedings of EPAC 2002, Paris, France, p. 1497.

• E. Benedetto, E. Benedetto
  Politecnico di Torino, Torino
• G. Franchetti
  GSI, Darmstadt
• K. Ohmi
  KEK, Ibaraki
• D. Schulte, F. Zimmermann
  CERN, Geneva

• D. Schulte, G. Arduini, V. Baglin, J.M. Jimenez, F. Zimmermann
  CERN, Geneva

• P.A. Seidl, D. Baca, F.M. Bieniosek, J.-L. Vay
  LBNL, Berkeley, California
• R.H. Cohen, A. Friedman, D.P. Grote, M. Kireeff Covo, S.M. Lund, A.W. Molvik
  LLNL, Livermore, California

Accelerators for inertial fusion energy, high-energy density physics and other high intensity applications have an economic incentive to minimize the clearance between the beam edge and the aperture wall. This increases the risk from electron clouds and gas desorbed from walls. Using the High Current Experiment at LBNL, we have measured the beam (0.18 A, 1 MeV K+ ) distribution upstream and downstream of a short lattice of magnetic quadrupoles where the 2·rms beam size is =50% of the quadrupole aperture, and the generalized perveance is ˜10-3. Between magnets, the transverse beam distribution is also imaged. The beam potential is 1-2 kV, large enough to trap electrons produced by, for example, K+ - gas collisions. Gas and electron effects are intentionally induced by varying gas pressure and the bias of e^- controlling electrodes.* The measurements are compared to WARP PIC simulations that include the self-consistent tracking of electrons and ions.**

*A. W. Molvik et al., this conference. **J-L Vay et al., this conference.

• J.-L. Vay, M.A. Furman
  LBNL, Berkeley, California
• R.H. Cohen, A. Friedman, D.P. Grote
  LLNL, Livermore, California

We present initial results from the self-consistent beam-cloud dynamics simulations of a sample LHC beam, using a newly developed set of modeling capability based on a merger of the three-dimensional parallel Particle-In-Cell accelerator code WARP and the electron cloud code POSINST.*,** Although the storage ring model we use as a test bed to contain the beam is much simpler and shorter than the LHC, its lattice elements are realistically modeled, as is the beam and the electron cloud dynamics. The simulated mechanisms for generation and absorption of the electrons at the walls are based on previously validated models available in POSINST.***

*J.-L. Vay, these proceedings. **J.-L. Vay, Proc. "ECLOUD04," Napa (California), 2004. ***M.T.F. Pivi and M.A. Furman, Phys. Rev. STAB, PRSTAB/v6/i3/e034201.

• J. Wu, T.O. Raubenheimer
  SLAC, Menlo Park, California

In a linear collider, sources of beam jitter due to kicker noise, quadrupole vibration and long-range transverse wakefields will lead to beam offsets and tilts at the Intersection Point (IP). In addition, sources of emittance dilution such as short-range transverse wakefields or dispersive errors will lead to internal beam distortions. When the IP disruption parameter is large, these beam imperfections will be amplified by a single bunch kink instability which will lead to luminosity loss. In this paper, we study the luminosity loss and then the optimization required to cancel the luminosity loss first analytically and then with simulation.

• J. Wu, A. Chao, T.O. Raubenheimer, A. Seryi
  SLAC, Menlo Park, California
• C.K. Sramek
  Rice University, Houston, Texas

In a linear collider, sources of emittance dilution such as transverse wakefields or dispersive errors will couple the vertical phase space to the longitudinal position within the beam (the so-called ‘banana effect'). When the Intersection Point (IP) disruption parameter is large, these beam distortions will be amplified by a single bunch kink instability which will lead to luminosity loss. We study this phenomena both analytically using linear theory and via numerical simulation. In particular, we examine the dependence of the luminosity loss on the wavelength of the beam distortions and the disruption parameter. This analysis may prove useful when optimizing the vertical disruption parameter for luminosity operation with given beam distortions.

• P. Stoltz, A. Prideaux
  Tech-X, Boulder, Colorado

We have implemented an R-matrix close coupling approach to calculate capture, ionization, stripping and excitation cross-sections for 0.5 to 8.0 MeV K+ incident on Ar. This is relevant to the High Current Experiment at Lawrence Berkley National Laboratory. These cross sections are used to model accelerator particle dynamics where background gasses can interfere with beam quality. This code is a semi-classical approach that uses quantum mechanics to describe the particle interactions and uses classical mechanics to describe the nuclei trajectories. We compare a hydrogenic approximation for K+ with a pseudo-potential approach. Further we are developing a variational approach to quickly determine the best pseudo-potential parameters. Since many R-Matrix computationalists use this pseudo-potential approach, this approach will be useful for helping generate cross sections for any collision system.

• S.A. Veitzer, P. Stoltz
  Tech-X, Boulder, Colorado
• R.H. Cohen, A.W. Molvik
  LLNL, Livermore, California
• J.-L. Vay
  LBNL, Berkeley, California

• B. Feng, A.F. Ghalam, T.C. Katsouleas
  USC, Los Angeles, California
• E. Benedetto, F. Zimmermann
  CERN, Geneva
• V.K. Decyk, W.B. Mori
  UCLA, Los Angeles, California

• L. Wang, H.-C. Hseuh, Y.Y. Lee, D. Raparia, J. Wei
  BNL, Upton, Long Island, New York
• S.M. Cousineau, S. Henderson
  ORNL, Oak Ridge, Tennessee

The beam loss along the Spallation Neutron Source’s (SNS’s) accumulator ring is mainly located at the collimator region. From the ORBIT simulation, the peak power deposition at the three collimators is about 500, 350 and 240 W/m, respectively. Therefore, a sizeable number of electrons may be accumulated at this region due to the great beam loss. This paper simulated the electron cloud at the collimator region and the possible remedy.

• R.C. Davidson, S.R. Hudson, I. Kaganovich, H. Qin, E. Startsev
  PPPL, Princeton, New Jersey

In application of heavy ion beams to high energy density physics and fusion, background plasma is utilized to neutralize the beam space charge during drift compression and/or final focus of the ion beam. It is important to minimize the deleterious effects of collective instabilities on beam quality associated with beam-plasma interactions. Plasma electrons tend to neutralize both the space charge and current of the beam ions. It is shown that the presence of the return current greatly modifies the electromagnetic Weibel instability (also called the filamentation instability), i.e., the growth rate of the filamentation instability greatly increases if the background ions are much lighter than the beam ions and the plasma density is comparable to the ion beam density. This may preclude using underdense plasma of light gases in heavy ion beam applications. It is also shown that the return current may be subject to the fast electrostatic two-stream instability.

• I. Kaganovich, R.C. Davidson, E. Startsev
  PPPL, Princeton, New Jersey

Ion-atom ionization cross sections are needed in many applications employing the propagation of fast ions through matter. When experimental data or full-scale theoretical calculations are non-existent, approximate methods must be used. The most robust and easy-to-use approximations include the Born approximation of quantum mechanics and the quasi-classical approach utilizing classical mechanics together with the Bohr-Sommerfeld quantization rule.* The simplest method to extend the validity of both approaches is to combine them, i.e., use the two different approaches but only for the regions of impact parameters in which they are valid, and sum the results to obtain the total cross section. We have recently investigated theoretically and experimentally the stripping of more than 18 different pairs of projectile and target atoms in the range of 3-38 MeV/amu to study the range of validity of various approximations. The results of the modified approach agree better with the experimental data than either the Born approximation or the quasi-classical approach, applied separately.

*I. D. Kaganovich et al., "Formulary and scaling cross sections for ion-atom impact ionization," http://arxiv.org/abs/physics/0407140.

• I. Kaganovich, R.C. Davidson, E. Startsev
  PPPL, Princeton, New Jersey

Background plasma can be used as an effective neutralization scheme to transport and compress intense ion beam pulses, and the application of a solenoidal magnetic field allows additional control and focusing of the beam pulse. Ion beam pulse propagation in a background plasma immersed in an applied solenoidal magnetic field has been studied both analytically and numerically with three different particle-in-cell codes (LSP, OOPIC-Pro and EDPIC) to cross-check the validity of the results. Very good charge and current neutralization is observed for high values of the solenoidal magnetic field.* However, for intermediate values of the solenoidal magnetic field, current neutralization is a complex process, and a sizable self-magnetic field is generated at the head of the beam. Collective wave excitations are also generated ahead of the beam pulse.

*I. D. Kaganovich, E. A. Startsev and R. C. Davidson, Nuclear Instruments and Methods in Physics Research A, in press (2004).

• H. Qin, R.C. Davidson, S.R. Hudson, E. Startsev
  PPPL, Princeton, New Jersey

The collective effects in high-intensity 3D bunched beams are described self-consistently by the nonlinear Vlasov-Maxwell equations.* The nonlinear delta-f method,** a particle simulation method for solving the nonlinear Vlasov-Maxwell equations, is being used to study the collective effects in high-intensity 3D bunched beams. The delta-f method, as a nonlinear perturbative scheme, splits the distribution function into equilibrium and perturbed parts. The perturbed distribution function is represented as a weighted summation over discrete particles, where the particle orbits are advanced by equations of motion in the focusing field and self-consistent fields, and the particle weights are advanced by the coupling between the perturbed fields and the zero-order distribution function. The nonlinear delta-f method exhibits minimal noise and accuracy problems in comparison with standard particle-in-cell simulations. A self-consistent 3D kinetic equilibrium is first established for high intensity bunched beams. Then, the collective excitations of the equilibrium are systematically investigated using the nonlinear delta-f method implemented in the Beam Equilibrium Stability and Transport (BEST) code.

*R.C. Davidson and H. Qin, Physics of Intense Charged Particle Beams in High Energy Accelerators (World Scientific, 2001). **H. Qin, Physics of Plasmas 10, 2078 (2003).

• V.G. Dudnikov, G. Dudnikova
  BTG, New York

• M. Kireeff Covo, J.J. Barnard, R.H. Cohen, A. Friedman, D.P. Grote, S.M. Lund, A.W. Molvik, G.A. Westenskow
  LLNL, Livermore, California
• D. Baca, F.M. Bieniosek, C.M. Celata, J.W. Kwan, P.A. Seidl, J.-L. Vay
  LBNL, Berkeley, California
• J.L. Vujic
  UCB, Berkeley, California

The cost of accelerators for heavy-ion inertial fusion energy (HIF) can be reduced by using the smallest possible clearance between the beam and the wall from the beamline. This increases beam loss to the walls, generating ion-induced electrons that could be trapped by beam space charge potential into an "electron cloud," which can cause degradation or loss of the ion beam. In order to understand the physical mechanism of production of ion-induced electrons we have measured impact of K+ ions with energies up to 400 KeV on stainless steel surfaces near grazing incidence, using the ion source test stand (STS-500) at LLNL. The electron yield will be discussed and compared with experimental measurements from 1 MeV K+ ions in the High-Current Experiment at LBNL.*

*A.W. Molvik et al., PRST-AB 7, 093202 (2004).

• S.M. Lund
  LLNL, Livermore, California
• S. R. Chawla
  UCB, Berkeley, California

It has been observed in both experiment and particle in cell simulations that space-charge-dominated beams suffer strong emittance growth in alternating gradient quadrupole transport channels when the undepressed phase advance σ0 increases beyond about 80 degrees per lattice period. Transport systems have long been designed to respect this phase advance limit but no theory has been proposed to date to explain the the cause of the limit. Here we propose a mechanism to parametrically explain the transport limit as being due to classes of halo particle orbits moving close to the beam edge in phase-space when σ0 increases beyond 80 degrees. A finite beam edge and/or perturbation acting on an edge particle can then act to move edge particles to large amplitude and lead to large increases in beam phase space area, lost particles, and degraded transport. A core particle model for a uniform density elliptical beam in a periodic focusing lattice was written and is applied to parametrically analyze this process for both periodic alternating gradient quadrupole and solenoidal transport lattices. Self-consistent particle in cell simulations are also carried out to support results.